Fuel supply devices for supplying liquefied gas fuel to a combustion chamber of an engine are conventionally known. One example of such a fuel supply device includes a feed pump that sends fuel from a fuel tank to a high pressure pump. The fuel is compressed by the high pressure pump, sent through a common rail, and supplied into the combustion chamber of the engine by an injector.
Such a high pressure pump is known to include a camshaft, a cam, a housing, a cam reception hole, and a seal member, as explained below.
The camshaft is driven by an internal combustion engine to rotate.
The cam disposed on the camshaft that drives a plunger.
The housing houses the cam, and forms a cam chamber that receives fuel for lubricating the cam.
The camshaft reception hole is formed in the housing and penetrates from inside of the cam chamber to outside of the cam chamber. The camshaft is inserted into the camshaft reception hole, and is retained by the camshaft reception hole.
The seal member prevents fuel in the cam chamber from leaking outside through the camshaft reception hole.
Fuel is supplied to the cam chamber in liquid form to lubricate the cam. In such a case, the pressure inside the cam chamber is high, especially if the fuel is a liquefied gas fuel.
In this regard, a known technique is to provide the seal member in two stages so as to prevent fuel from leaking out of the housing. In other words, two seal members are provided on an outer periphery of the camshaft within the camshaft reception hole. These two seal members are spaced away from each other in an axial direction.
Of these two seal members, a first seal member is closer toward the cam chamber, and a second seal member is farther from the cam chamber. A gap between the first seal member and the second seal member is referred to as an inter-seal space.
However, even if the seal member is provided in two stages in this manner, the pressure limit of each seal member is limited. If the first seal member is unable to withstand the pressure in the cam chamber, the fuel will pass through the first seal member and leak into the inter-seal space. Then, the pressure in the inter-seal space will rise, and may ultimately result in the fuel passing through the second seal member to leak to the outside.
JP 2003-206825 A discloses a technique of connecting the inter-seal space to a purge tank to collect fuel in the purge tank. However, this technique lacks versatility with respect to devices that do not include a purge tank.
Accordingly, it is preferable to collect fuel in a fuel tank, which is always provided. However, if the fuel tank is simply connected to the inter-seal space, the pressure in the fuel tank is high, and thus it may be difficult to collect the fuel.
Further, if the fuel tank is simply connected to the inter-seal space, the maximum allowable pressure of the fuel tank may be applied on the seal members. Accordingly, if the pressure limit of the seal members is not designed to withstand the maximum allowable pressure of the fuel tank, then fuel may actually leak from the fuel tank instead. However, the maximum allowable pressure of the fuel tank is generally very high, and therefore it may be unrealistic to design such a seal member.
Accordingly, in order to collect fuel in the fuel tank, instead of simply connecting the fuel tank to the inter-seal space, an appropriate solution is needed.